Relaxation circuits for producing electrical impulses at regular recurrence frequencies



March 30, 1948. M. DODDS ET AL 2,438,845

RELAXATION CIRCUITS FOR PRODUCING ELECTRICAL IMPULSES AT REGULAR RECURRENCE FREQUENCIES Filed Dec. 18, 1943 2 Sheets-Sheet 1 f k Carrenl /4nade H66- C'aiizade v HT /G7ld v 1 'March 30, DQDDSA r A 2,438,845

RELAXATION CIRCUITS FOR PRODUCING ELECTRICAL IMPULSES AT REGULAR RECURRENCE FREQUENCIES Filed Dec. 18;,1945 2 Sheets-Sheet 2 'OHN MATHIESO'N DODDS mam JOHN SCOLES ATTORNEYS Patented Mar. 30, 1948 nE AxA'rIoN CIRCUITS ,Fon PRODUCING ELECTRICAL IMPULSES AT REGULAR RE- OURRENCEFREQUENCIES John Mathieson Dodds, Timperley, and Graham John Scoles, East Sheen, London, England, as- ,signors to.Metropolitan-Vickers Electrical Company'Llmited, London, England, a company of Great Britain Applica'tionbecember 18, 1943, Serial No. 514,866 *In Great Britain June 26, 1942 Section 1, 'Public'Law 690, August 8, 1946 Patent expires June 26, 1962 4 Claims. 1

This invention relates to relaxation circuits for producing electrical impulses at regular recurrence irequencies, more particularly, but not exclusively, forthe impulsi-ng of the tripping electrodes of the spark gap device forming inter alia the subject of icopendlng United States applications all filed December 18, 1943, ,SerialNo. 514,- 86-3, now Patent 'No. 2,400,456, issued'May 14, 1946; Serial No. 514,864, now Patent No. 2,400,457, issued May 14, 1946; :Serial No. 514,865, now Patout No. 2,433,755, issued December 30, 1947, the main electrodes of the spark gap being preferably supplied with energy through the circuits diagrammatically illustrated by Figs. 1, 2and 3 of the drawings cf said .copending applications, serial Nos. 514,863 and 514,864 respectively, whilst the tripping is .efiected through a valve having a small inductance in its anode circuits and having its control grid supplied with positive-going? impulses from the relaxation oscillator, which heretofore has been per se as described, for use in producing vstrobosi'zopic illumination, in Free. I. R. E., November 1939,. :Saidrela'xation oscillator comprises basically a valve having between its cathode and the negative terminal of the anode supply, a timing circuitof resistance R and parallel capacityC whereby the control grid bias is varied through the secondary of an impulse transformer'the primary of which-is -appropriately connected between the valve anode "and the positive terminal :of the anode supply such that the operation of thecircuit isas hereinafter described.

Whilst the present invention will be hereinafter described mainly as an addition .to the relaxation oscillator circuit described in the last sentence :of the preceding paragraph 11; is to be understood that the invention may be applied to other forms of relaxation oscillatonsuch, for example, as Thyratron ta British registered trade-mark) and flip-flop" circuits.

The present invention comprises the addition to the per se known relaxation oscillator circuit of a rectifier, such as a diode, in series with an inductance, the latter combination resonating with a condenser at one-hali1the required recurrence frequency and being connected, such as in the several ways hereinafter described, eflectively in series with the relaxation oscillator circuit so that the rectifier by the prevention of current reversal causes a very rapid change of potential, as will be hereinafter explained, whereby more accurate timing between successive pulses is obtainable-than with the known arrangements of relaxation circuits.

it will now be described with reference to the accompanying drawings, Figure 1 of which is a circuit diagram of the known form of relaxation oscillator published in Proc. I. R. E., November 1939, and Figure 2 is a group of graphs indicating various wave forms of electrical quantities operating in the circuit shown in Figure 1;

Figure 3 is a diagram of one circuit arrangement in accordance with the invention, and Figure 4 is a group of graphs indicating the wave forms of electrical quantities which obtain during the operation of the circuits shown in Fi ure '3;

Figure 5 is a circuit diagram of a modification of the arrangement shown in Figure 3, and Figure 6 is a group of graphs indicating the wave forms of potentials at certain points indicated on the circuit of Figure 5;

Figure 7 is a diagram of a further modification of the circuit, still employing the relaxation oscillator per se generally as shown in Figure 1, and Figure 8 is a group of graphs similar to those shown in Figure 6, but relative to the circuit of Figure 7, and

Figure 9 is a circuit diagram showing themvention applied to a Thyratron relaxation oscillator.

Referring first to the known arrangement illustrated in Figure 1, the triode or other suitable hard valve V has between its cathode and the negative terminal of the high tension supply, the timing circuit comprising the resistance R and parallel capacity C whereby the control grid bias is varied through the secondary S of the impulse transformer the primary P of which is ap propriately connected between the anode of the valve V and the positive terminal of the anode supply, the anode thus having an inductive load LP as indicated in dotted lines. The operation of the circuit shown in Figure 1 is as follows:

Assume that the condenser C has been. charged during the preceding cycle such that the gridcathode potential biases the valve V beyond the cut-oil point. In this condition no current can pass through the valve and no voltage can be developed across the primary or secondary Winding of the transformer, so that the anode voltage on the valve is that of the high tension positive supply. The charge on the condenser C leaks away through the resistance R until the impedance of the valve between anode and cathode is nolonger infinite, due to the grid bias passing the cut-oil. point, at the instant of which the P I 1 grid is still negative to the cathode so that no To enable the invention to be fully understood vlitv current can flowin the secondary winding of the 4 oscillator. Whereas in the, arrangement'shown in Figure 1 the voltage-impulses which may be applied to the valve, which in turn generates impulses for the trigger electrode of the spark gap,

are taken from the terminal Q, this is inconvenient-in the arrangement shown in Figure 3 on account of the locking wave form so that a mitting an anode current of the same magnitude also to flow. The process continues until the anode voltage becomes too low to maintain the relationship of anode and grid currents as enforced by transformer action. At this point the sense of the transformer voltages will reverse,--

thus cutting off grid and anode currents almost tertiary winding T on the transformer is provided. I

With regard to the arrangement shown in Figure 3 the part of the circuit comprising V, P, S, R and C operates as described with reference to Figures 1 and 3, so that the condensers C and Ca become charged in series and their separate wave forms are indicated in the uppermost graph of Figure4. After the pulse the condenser 0 discharges through the resistance R as previously instantaneously. And since the sum of the grid and anode currents will have been charging the condenser C during this period, the system immediately returns to its initial (cut-01f) condition. At'the same time the sudden cessation of current through the primary inductance LP of the transformer causes the energy stored in it during the conducting part of the cycle to reappear'as a violent overswing, this voltage also appearing, of course, on the secondary winding of the transformer, in the reverse sense, and causing the valve current to be cut off very suddenly.

In the uppermost graph of Figure 2 the part ab represents the charge of the condenser C leaking away through the resistance R, namely until the impedance of the valve between anode and cathode is no longer infinite, the part be of the curve indicates the conducting period during which the condenser is charged by the sum of the grid and anode currents of the valve. Thereafter the charge leaks away as indicated by the part cd of the curve. Thereafter the cycle is repeated. The middle graph of Figure 2 indicates (on a different time scale) the wave form of one cycle of the anode voltage, starting from the point of time b in the uppermost curve, whilst the two curves in the lowermost graph of Figure 2 indicate (on this same time scale) the wave forms of both the grid and cathode voltages during the same cycle commencing at the same point of time.

The known relaxation oscillator above described is satisfactory in so far as it produces impulses sufficient to operate the aforesaid spark gap, but the timing circuit RC may not give under some conditions sufiiciently accurate timing between successive pulses, a defect which may be accentuated in the presence of strong fields. An object of the present invention is a modification of the above described relaxation oscillator whereby very accurate spacing of the pulses can be obtained such as is required when the aforesaid sparkgap is used in connection with radiolocation of the pulse modulation type.

Referring to the arrangement according to the present invention shown in Figure 3, the upper part of the diagram may be considered as'identical with that shown in Figure 1-, and in the arrangement shown in Figure 3 there is added to the lower end'of the resistance R the anode of diode D, the cathode of which is connected through the inductance LR to the negative terminal of the high tension supply. A condenser CR is connected across the diode D and inductance LR, as shown. The values of Laand Ca are so chosen that the natural frequency of the-resonant circuit they form is half that of the recurrent frequency of the pulses'to beiproduced by:.the

whilst the condenser Ca discharges through the rectifier D and inductance LR as shown by the curve ,fgm. The corresponding current Wave form 7791 is similar to that of an ordinary resonant circuit-except that due to the presence of the.

diode D current reversal is impossible. Thus the voltage at the junction of the diode cathode and the inductance LR collapses rapidly to zero at this moment, as shown by the line ml, this change in potential being applied to the grid of the valve V through the winding S. If the value of the resistance R is correctly chosen the valve con- In this ducts once more and the cycle repeats. way the period between successive impulses is accurately determined over a wide range of the setting of the value of the resistance R.

It is to be appreciated that the graphs in Figure 4 do not show the wave forms when the circuit is in look with LR'and CR since under these conditions the point h is almost exactly coincident with the point m, which would make the graph difiicult to follow. It will be appreciated, furthermore, that the current wave form y'lcl would be sinusoidal, except that, due to the presence of the diode, the current reversal is prevented and the voltage on the grid of the valve V collapses very rapidly to zero, thus raising in a positive sense the voltage of the grid of this valve with respect'to its cathode, as'aforesaid.

Referring next to Figure 5 of the drawings, the arrangement therein illustrated differs only from that shown in Figure 3 in that thediode D and its series inductance LR are connected between the high tension positive supply and the primary winding P of the impulse transformer, the cathode of the diode D being connected through a condenser Co in series with a resistance Re to the-grid of the valve V. The additional condenser CR is connected between themductance LR and the negative terminal of the high tension supply.

In Figure 6 the' graph Vc shows the Wave form of the voltage on the cathode of the valve V, the graph'LR' the voltage at the lower end of the inductance LR and the graph Dc the voltageof the cathodeof the diode D5 {The third 'arrangem'ent'J-shown"in 7:

pulse to the cathode of valve-V. This is, of course,

equivalent to applying a positive impulse to the control grid.

In Figure 8 the graph Dc represents the voltage wave form of the cathode of the valve V, the graph LlR, shows the wave form of the lower" end of the inductance La, whilst the graph Da represents the Wave form of the anode of the diode D.

Finally in the arrangement shown in Figure 9 the anode of the Thyratron VT is connected through the optional anode inductance LP, and resistance r to the H. T.+ supply, a condenser C being connected between the junction of inductance LP and r and H. T.. The cathode of the Thyratron, as before, has connected to it the variable resistance R in parallel with the condenser C, and the lower end of this circuit is connected to the negative high tension terminal through the diode D and series inductance La, the cathode of the diode being connected through a resistance Rg to the grid of the Thyratron VT.

We claim:

1. A relaxation circuit for producing electric impulses at regular recurrence frequencies, comprising a relaxation oscillator including an electric discharge tube having an anode, cathode and control grid, positive and negative supply lines for said anode and cathode respectively, a resonant circuit having a resonant frequency half the recurrent frequency comprising an inductance and con-denser in parallel connected between the oathode of said discharge tube and the negative supply line, a diode in the inductive branch of said resonant circuit and connected in the same sense as said discharge tube, and means including a connection between the positive end of said inductance and the grid of said discharge tube whereby said diode prevents reversal of current in the inductance and a positive potential is thereby applied to said grid to initiate an impulse.

2. A relaxation circuit for pIOClllClIlg electrical impulses at regular recurrence frequencies, comprising a relaxation oscillator including an inductance effectively connected in circuit therewith, and means including a rectifier and a condenser with which said rectifier and inductance resonate at one-half the frequency of said relaxation oscillator for preventing current reversal in the inductance and thereby causing rapid change of potential at the input of said oscillator to initiate an impulse.

3. A relaxation circuit for producing electrical impulses at regular recurrence frequencies, comprising a relaxation oscillator including an inductance effectively connected in circuit therewith, and means including a diode and a condenser connected across said diode and with which said diode and inductance resonate at onehalf the frequency of said relaxation oscillator for preventing current reversal in the inductance and thereby causing rapid change of potential at the input of said oscillator to initiate an impulse.

4. A relaxation circuit for producing electrical impulses at regular recurrence frequencies, comprising a relaxation oscillator including an inductance effectively connected in circuit therewith, and means including a diode and a condenser connected to said inductance to form a resonant circuit resonating at one-half the frequency of said relaxation oscillator for preventing current reversal in the inductance and thereby causing rapid change of potential at the input of said oscillator to initiate an impulse.

JOHN MATHIESON DODDS. GRAHAM JOHN SCOLES.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

